1. Field of the Invention
The present invention relates to a tablet made of a resinous material such as a plastic and adapted for resin-molding semiconductor devices such as semiconductor integrated circuits (referred to as "IC" hereinafter), as well as to a method of producing such a tablet. The invention also is concerned with an improved resin-molding method for resin-molding semiconductor devices by making use of the tablet.
2. Description of the Related Arts
FIG. 11 shows in section one example of a conventional tablet forming machine of the type disclosed in Japanese Patent Application Laid-Open No. 59-139633. The tablet forming machine shown in FIG. 11 has a cylinder 1, a compression piston 2 slidingly received in the bore of the cylinder 1 for compressing powdered resin, and a pusher piston 3 which also is slidingly received in the bore of the cylinder 1 in an opposed relation to the compression piston 2 for pushing a tablet, which has been formed under compression by the compression piston 2, to the outside of the cylinder 1. The pistons 2 and 3 are provided with "O" rings 4 and 5 which are fitted on their outer peripheral surfaces for providing seals between the outer peripheral surfaces of these pistons 2, 3 and the inner peripheral surface of the cylinder 1. The tablet forming machine further has a hopper 6 which is connected to a supply port 1a formed in a portion of the wall of the cylinder 1 for charging the powdered resin into the cylinder 1, and a vacuum pump 7 which is connected through a conduit 8 to a discharge port 1b which also is formed in the wall of the cylinder 1 in a spaced apart relation to the supply port 1a in the longitudinal direction of the cylinder 1. The vacuum pump 7 exhausts air from a chamber, which is defined by the pistons 2 and 3 in the cylinder 1, through the discharge port 1b and the conduit 8 so as to establish vacuum in the chamber.
In operation, the piston 2 is retracted to the left as viewed in FIG. 11 to a position where it does not block the supply port 1a and a metered amount of a powdered resin 9 is charged into the cylinder 1 from the hopper 6 through the supply port 1a. The powdered resin is, although not exclusively, a mixture of particles or powders of an epoxy resin and an inorganic filler.
Then, after the piston 2 has been moved to the right as viewed in FIG. 12 to a position intermediate between the supply port 1a and the discharge port 1b, the vacuum pump 7 is started to exhaust air from the chamber in the cylinder 1 through the discharge port 1a, thereby to establish a reduced pressure in the cylinder 1.
Subsequently, the piston 2 is further moved to the right so as to compress the powdered resin at a pressure of, for example, 1,000 kg/cm.sup.2. Consequently, any voids or minute spaces between the particles of the powdered resin 9 are collapsed so that the air trapped there is expelled and is discharged to the outside of the cylinder 1 through the discharge port 1b.
It is thus possible to form, by compression forming method, a tablet in which adjacent particles are densely arranged to closely contact with one another so as to minimize air involved.
The tablet 11 thus formed, however, still has minute internal pores or spaces which communicate with similar pores or spaces in the outer region of the tablet through numerous minute pores, because the particles are merely compacted by mechanical compression force. These continuous pores, though they are very fine, are immediately refilled by air when the pusher piston 3 is moved to the left as viewed in FIG. 12 to force the formed tablet 11 outside the cylinder 1 from the left end opening of the cylinder 1. In consequence, numerous intergranular air 10, i.e, pores filled with air, are formed in the final product of the tablet, as shown in FIG. 13.
When this tablet 1 is used for the purpose of packaging an IC chip as shown in FIG. 14 so as to form an IC product, the intergranular air 10 trapped in the tablet 11 is released into the spaces in the package to generate voids in the package, so that various inconveniences are caused such as deterioration of the performance of the IC 12 and degradation of appearance of the IC product due to presence of voids on the package outer surface, resulting in a lower yield of the product.